Tripod type constant velocity joints are well known in the automobile industry as one type of constant velocity joints used in the drive system of automobiles to transfer a uniform torque and a constant speed, while operating with a wide range of joint angle.
For instance, one example of the tripod type constant velocity joint was illustrated in Japanese Patent Application, S62-233522.This tripod type constant velocity joint typically includes tripod fixed to an end of the second rotating shaft, which functions as a driven member, and hollow cylindrical housing fixed to an end of the first rotating shaft which functions as a drive member. Three circumferential grooves are formed at three locations on the inner face of the housing at equal spacing in the circumferential direction and extend in the shaft direction of the housing. Each tripod comprises a boss connected to the second rotating shaft, and each trunnion has a cylindrical shape and extends radially from three locations at equal spacing around the boss. Each trunnion has a roller fixed at a distal end of the trunnion and with needle rollers engaged therein. In this arrangement, each roller can freely rotate about the trunnion while also be displaced in the axial direction of the trunnion. The constant velocity movement between the first and second rotating shafts is ensured with the rollers rotatably and displaceably engaging in the grooves disposed along the inner face of the housing. In order to facilitate the sliding movement, a pair of side faces are formed in circular recesses on each side of the respective grooves, and each roller is supported rotatably and pivotally along the side faces of the grooves.
When the first and second rotating shafts rotate with a joint angle present between the first and second shafts, each roller moves with complexity. For example, each roller moves in the axial direction of the housing along each of the side faces of the respective guide grooves, while the rollers change in orientation and further displace in the axial direction of the trunnion. Such movement of the rollers cannot cause a relative movement between a peripheral outside face of each of the rollers and each of the side faces to be smoothly made. Thus, a relatively large friction occurs between the faces. As a result, this tripod type constant velocity joint produces three-directional axial forces as the shafts rotate. In the application of a prior art tripod joint to the vehicles, it is known that the axial forces may cause a transverse vibration typically referred to as “shudder”. This shudder disturbance may become severe particularly when a large torque is transmitted with a relatively large joint angle present.
In order to restrain or reduce such conventional shudder phenomena, various suggestions have been introduced. Among various attempts, the inventors of this application have particularly discovered that the conventional shudder problem can be reduced by providing sufficient lubrication channels in the contact surfaces between the convex outer surface of the roller and the corresponding inner surface of respective guide grooves of the housing and also by optimally controlling the distribution of the contact force and/or the contact angle between the roller and the corresponding contact groove of the housing.
FIG. 1 illustrates an example of a conventional constant velocity joint, which includes a housing 12 of an outer joint member (i.e., a driving member), and three radially-projecting trunnions 16 of an inner joint member (i.e., a driven member) internally coupled within respective guide groove of the housing 12. Each trunnion 16 is received within a roller assembly which is composed of outer roller 13, inner roller 14, and multiple needle bearings 15 engaged between the outer and inner rollers 13 and 14. As shown, the guide groove has a circular cross-sectional shape with a surface radius Rg, and the outer surface of the outer roller 13 similarly has a circular cross-sectional shape with a surface radius Rrx (in the cross section taken along the axis of the trunnion 16 or the outer roller 13, as shown in the upper drawing of FIG. 1). The radius Rrx of the outer roller 13 is a little smaller than the radius Rg of the housing 12, thus leaving a clearance “S” there-between, which is necessary in order to manufacture and assemble the apparatus. In addition, lubricants (e.g., grease) can be filled in this clearance “S” for lubrication and to reduce frictions in the contact areas. As shown in the lower drawing of FIG. 1, the outer roller 13 further includes another circular cross-sectional shape with a surface radius Rry (in the cross section taken in orthogonal direction relative to the axis of the trunnion 16 or the outer roller 13).
In operation, the trunnion 16 can be displaced radially and pivotally relative to the guide groove of the housing 12, and this movement of the trunnion 16 associated with the resultant friction with the roller assembly causes the outer roller 13 to move reciprocally in an axial direction (e.g., in the Y-axis direction in FIG. 1), in part, due to the presence of clearance “S”.
As illustrated in FIG. 2, when the outer roller 13 moves upwardly in the groove of the housing 13, the outer roller 1 3 contacts with the housing at “P1” on an upper portion of the housing groove with axial displacement δ and contact angle β defined therein. This causes the clearance S1 at upper portion 121c of the housing groove to be substantially narrowed while enlarging the clearance S2 at lower portion 122c of the housing groove. As a result, the grease filled in the upper clearance S1 squeezes out from the clearance and the contact friction increases substantially, and thus, causing to generate adverse vibrations or disturbance to the vehicle. As illustrated in FIG. 3, when the outer roller 13 moves downwardly in the groove of the housing 13, the outer roller 13 contacts with the housing at “P2” on a lower portion of the housing groove with its axial displacement δ and contact angle β defined thereby. This causes the clearance S2 at the lower portion of the housing groove to be substantially narrowed while enlarging the clearance S1 at the upper portion of the housing groove. As a result, the grease filled in the lower clearance S2 squeezes out from the clearance and the contact friction increases substantially, and thus, causing to generate adverse vibrations or disturbance to the vehicle. In the drawing, the undefined reference “O” is the center of the opposing housing grooves, and reference “Or” is the center of the displaced outer roller 13.